2 
BULLETIN 3 8, PUERTO RICO EXPERIMENT STATION 
among older -animals as well as among the young may occur. The 
lungworms also thrive, and where pigs are raised and fed in numbers 
for several years in succession, unless precautions are taken, they may 
increase sufficiently to cause financial losses instead of profits in this 
industry. There are other parasites which on many farms are ob- 
stacles to profitable swine production. 
Infestations with internal parasites, similar to those in other host 
animals, are more or less seasonal in occurrence. Among the animals 
slaughtered at Mayaguez, worm parasites are most common during 
a period of several months beginning with December. One-half or 
more of these hogs are obtained from the dry southern coastal plain. 
In the dry sections the bulk of the infestations are picked up during 
the latter part of the rainy season, whereas in the areas subject to 
torrential showers they occur at different times during the so-called 
dry season. However, infestations may occur at any time among 
pigs closely confined in insanitary, covered pens or heavily shaded 
yards where the free-living stages of parasites are less influenced 
by the prevailing weather conditions where they would be out in the 
open. Other things being equal, the dry areas are superior to other 
parts of the island for raising pigs, as the environment is less favor- 
able for parasites. 
DAMAGE BY PARASITES 
Some of the external parasites extract blood from the host and 
all of them irritate the skin. The internal parasites of the pig cause 
damage by mechanically injuring tissues and organs and in various 
other ways. Pigs and young hogs are more susceptible and more 
seriously injured than older animals. Parasitism prevents the best 
and most rapid development and reduces vitality and resistance so 
that infested animals become susceptible to attack by other diseases. 
Heavy infestations with worms also indicate that the environment is 
insanitary and unsafe, and that other filth-borne diseases are likely 
to occur. 
SHADE 
Hogs must have shade, but the kind and extent of the cover is 
most important in a climate such as exists in Puerto Rico. A satis- 
factory structure for providing both shade and shelter consists of a 
framework about 4 feet high made of posts and poles and having the 
roof thatched or covered with sheet iron or palm leaves. This 
structure should be open on all four sides. Preferably the roof 
should be set on rollers and moved back and forth over its own 
length every few days, so that the entire area can be exposed periodi- 
cally to the direct rays of the sun. 
Dense, natural shade for yards should be avoided. The common 
practice of placing yards and feeding places under mango trees 
or other large trees having thick foliage is conducive to heavy infes- 
tations with parasitic worms. Sunshine is not only necessary for 
growing pigs, but it also acts as an efficient drier and disinfectant 
and is very destructive to the eggs and larvae of parasites on the 
ground. Also much of the island is exposed to seasonal and almost 
daily torrential showers. These rains have a very noticeable effect 
in washing and cleansing infective material from the soil. In many 
